The reliability of cone density measurements in the presence of rods

Abstract

Purpose: Recent advances in adaptive optics scanning light ophthalmoscopy (AOSLO) have enabled visualization of cone inner segments through nonconfocal split-detection, in addition to rod and cone outer segments revealed by confocal reflectance. Here, we examined the interobserver reliability of cone density measurements in both AOSLO imaging modalities. Methods: Five normal subjects (nine eyes) were imaged along the horizontal and vertical meridians using a custom AOSLO with confocal and nonconfocal split-detection modalities. The resulting images were montaged using a previously described semiautomatic algorithm. Regions of interest (ROIs) were selected from the confocal montage at 190 lm, and from split-detection and confocal montages at 900 and 1800 lm from the fovea. Four observers (three experts, one naïve) manually identified cone locations in each ROI, and these locations were used to calculate bound densities. Intraclass correlation coefficients and Dice’s coefficients were calculated to assess interobserver agreement. Results: Interobserver agreement was high in cone-only images (confocal 190 lm: 0.85; split-detection 900 lm: 0.91; split-detection 1800 lm: 0.89), moderate in confocal images at 900 lm (0.68), and poor in confocal images at 1800 lm (0.24). Excluding the naïve observer data substantially increased agreement within confocal images (190 lm: 0.99; 900 lm: 0.80; 1800 lm: 0.68). Conclusions: Interobserver measurements of cone density are more reliable in rod-free retinal images. Moreover, when using manual cell identification, it is essential that observers are trained, particularly for confocal AOSLO images. Translational Relevance: This study underscores the need for additional reliability studies in eyes containing pathology where identifying cones can be substantially more difficult.